The contamination of engine oils with the acidic byproducts of combustion is one of the major causes/drivers of engine corrosion and wear. Neutralization of these acidic species has conventionally been addressed by the addition of metal carbonate overbased detergents, such as calcium carbonate (CaCO3) overbased detergents, which have been found to be highly effective at neutralizing these acids. However, the use of highly overbased metal detergents has several drawbacks. Specifically, the incorporation of overbased metal detergents increases the sulfated ash (SASH) content of the lubricating oil compositions resulting in increased fuel consumption and exhaust back-pressure on after treatment devices such as diesel particulate filters.
Several attempts have been made to provide metal-free (ashless) sources of TBN that can be used as a replacement for at least a portion of the overbased metal detergent, however, these alternatives have achieved only limited success. US Patent Application 2007/0203031 suggests the use of low molecular weight, high TBN (total base number) succinimide dispersants as ashless TBN sources, however, these highly basic compounds have been found to have adverse effects on engine corrosion and on the fluoroelastomeric materials commonly used to form engine seals. U.S. Pat. Nos. 8,703,682; 8,143,201 and 9,145,530 suggest the use of phenylenediamine compounds, morpholine compounds and hindered amines, respectively, as ashless TBN sources for lubricating oil compositions.
Conflicting industry demands for lubricants having reduced sulfated ash contents (requiring reduced amounts of metal detergent overbasing) on the one hand, and lubricants having longer effective lives with increased acid-neutralizing capacity (requiring greater TBN contribution) on the other provide a strong need for ashless TBN sources that can be used as an alternative to conventional overbased metal detergents and provide a high level of acid neutralization.